The present invention relates in general to amplifiers and, more particularly, to an amplifier which combines a hyperbolic tangent transfer function with a hyperbolic sine transfer function to cancel distortion.
Amplifiers are commonly used in a myriad of applications to amplify an input signal and provide an amplified output signal. Amplifiers are often differential in operation. Typically end applications for differential amplifiers include radio frequency (RF) transceivers, cellular telephones, pagers, cordless telephones, filters, and other wireless communication equipment.
An important feature of differential amplifiers is to maintain linear operation over a wide range of input signal amplitudes. When operating in its linear range, a differential amplifier provides an output signal proportional to the input signal, where the proportionality is determined by the gain of the amplifier. Most prior art differential amplifiers operate linearly over a narrow range of input signal amplitudes. If the amplifier operates outside its linear range, then the output signal is subject to non-linear distortion and noise.
One prior art technique of increasing the linear range of the differential amplifier involves placing degeneration resistors in the emitters of the differential transistor pair. Unfortunately, the degeneration resistors also have the undesirable effect of decreasing the gain of the differential amplifier and increasing the noise figure.
Hence, a need exists for a differential amplifier having linear operation over a wide range of input signals with high gain and low noise figure.